Recovery of hydrocarbon material from a subterranean



2 Sheets-Sheet 1 INVENTORS M) BYJMJMJJ l ATTORNEY THEODORE W NELSON JAMES S. McNElL, JR.

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T. W. NELSON ETAL FORMATION BY IN-SITU COMBUSTION m da zoum RECOVERY OF' HYDROCARBON MATERIAL FROM A SUBTERRANEAN March 3l, 1964 Filed Nov. 20, 1959 Cl/JOSWW IELLVU NOIlOE/Nl HIV NELSON ETAL 3,126,953 EON MATERIAL FROM A SUBTERRANEAN BY IN-SITU COMBUSTION March 3l, 1964 T. W. RECOVERY OF HYDROOAR FORMATION 2 Sheets-Sheet 2 Filed NOV. 20, 1959 FIG. 2.

THEODORE W. NELSON JAMES S. McNlEL, JR.

INVENTORS wif/M MAMA ATTORNEY United States Patent Oli 3,126,953 Patented Mar. 31, 1964 ice RECOVERY F HYDROCARBN MATERIAL FROM A SUBTERRANEAN FRMATEUN BY lN-SITU COMBUSTHN Theodore W. Nelson, Westfield,` NJ., and James S. Mciel, Jr., Dallas, Tex., assignors to Soeony Mobil Gil Company, Inc., a corporation of New York Filed Nov. 20, 1959, Ser. No. 854,404 7 Claims. (Cl. 16d-i1) This invention relates to the recovery of hydrocarbon material from a subterranean formation by displacement of the hydrocarbon material within the formation by means of an injected fluid and relates more particularly to the recovery of hydrocarbon material from a subterranean formation by the method involving injection of an oxidizing fluid into the formation and combustion in place of a portion of the hydrocarbon material within the formation.

It has been proposed to recover hydrocarbon material from a hydrocarbon-containing subterranean formation by a method which involves combustion of a portion of the hydrocarbon material within the formation. In this method, termed in-situ combustion, oxidizing fluid is injected into the formation through an input well or wells. The formation is provided with an output well or wells and the array of the input well or wells and the output well or wells is termed the well pattern. Combustion of hydrocarbon material within the formation is initiated by suitable means. As the flow of oxidizing fluid to the formation is continued, a combustion front migrates through the formation. As this combustion front migrates through the formation, hydrocarbon material is displaced within the formation and advances into the direction of the output well or wells from which it is produced.

It has recently been realized that combustion will be maintained within the formation only when the rate of ilow of oxidizing fluid to the formation is suiiicient to effect a minimum rate of migration of the combustion front. It has recently been further realized that, on the other hand, there is a maximum rate of injection of oxidizing fluid which desirably should not be exceeded. This maximum rate of injection of oxidizing fluid is that which will effect migration of the combustion front at a rate such that the hydrocarbon material is displaced from within the formation at a rate no greater than it can be produced from the output well or wells.

Combustion is initiated within the formation at one of the wells forming the well pattern. The combustion front advances radially, or substantially radially, depending upon the number and position of the wells within the pattern, through the formation from this well. In the early stages of operation, the area of the combustion front is small and the minimum rate of advance of the combustion front effects a displacement of hydrocarbon material at a rate which is less than the rate at which it can be produced. However, in the later stages of operation, the area of the combustion front is large and a rate of advance of the combustion front greater than the minimum may effect displacement of hydrocarbon material at a rate which is greater than the rate at which it can be produced. Accordingly, from a practical standpoint, operations should be effected such that at first the rate of advance of the combustion front is in excess of the minimum but at the later stages is decreased in order that permissible rates of production of hydrocarbon material are maintained. Following this concept, since at first the area of the combustion front is small, the rate of injection of oxidizing Huid is also small. As the combustion front advances, its area increases and the rate of injection is increased in order to maintain the desired rate of advance. At the last stages, the area of the combustion front is at a maximum and the displacement of hydrocarbon material per unit advance of combustion front is also at a maximum. At this stage, the rate of injection is decreased. Accordingly, for any pattern of input and output wells, the rate of injection of oxidizing fluid is at rst low, is increased gradually thereafter to a maximum, and subsequently is decreased.

For any well pattern, the particular rates of injection of the oxidizing fluid Within the permissible limits will be determined, at least to some extent, by the economics of the installation and operation of the compressor or compressors employed for injection. With injection of oxidizing fluid at an increasing rate in the early stages and at a decreasing rate in the later stages, maximum cornpressor capacity is required only in the intermediate stages. Thus, in the early stages and the final stages, there is idle compressor capacity. This idle compressor capacity represents an economic loss and the loss is multiplied by the number of patterns that are being operated in a field at any one time.

It is an object of this invention to improve the economics of the in-situ combustion process. It is another object of this invention to decrease the cost of producing hydrocarbon material from a subterranean formation by iii-situ combustion. It is another object of this invention to use more fully available compressor capacity for in-situ combustion. It is another object of this invention to operate a plurality of well patterns with a saving in compressor capacity. Further objects of this invention will become apparent from the following detailed description.

In accordance with the invention, operations are carried out simultaneously but at different stages in a plurality of well patterns employing a common source of compressed fluid.

FIGURE 1 is a chart illustrating air injection rates with time according to an embodiment of the invention.

FIGURE 2 is a diagram of a well pattern illustrating the sequence of operations according to an embodiment of the invention.

In operations for the recovery of hydrocarbon materials from subterranean formations by procedures involving injection of a fluid, various well patterns are employed. These well patterns are known in the art. However, some description of these patterns is believed to be desirable. Typically, these well patterns comprise a central input Well, into which the fluid is injected, surrounded by a plurality of output wells from which the hydrocarbon material is produced. However, the well pattern may comprise one input well and one output well. There may be more than one input well. In the typical pattern, the number of output wells may vary. For example, the number of output wells may be 2, 3, 4, S, 6, 7, or 8, or more. The output Wells may be arranged in a regular geometric pattern about the central well or may be arranged unevenly about, and variously distanced from, the central input well. Ordinarily, in the United States, the five-spot well pattern is employed. In this pattern, the central injection well is surrounded by four equidistantly spaced output Wells. A seven-spot well pattern is also frequently employed although more so in countries other than the United States. In this pattern, the central injection Well is surrounded by six output wells arranged in a hexagon.

In the practice of the invention, the well patterns operated simultaneously may -be isolated patterns or developed patterns. An isolated pattern is defined as one which exists by itself from the standpoint that the direction of flow of the injected fluid through the subterranean formation from the input well to the output wells is not effected by the presence of the wells of any adjacent pattern. A developed pattern is defined as one which is part of a plurality of adjacent patterns, which may be similar or dissimilar, and the direction of flow of uid through the subterranean formation from the input well to the output well is effected by the wells of an adjacent pattern.

Reference will now be made to the accompanying drawings. In the drawings, operations are illustrated in connection with particular developed five-spot well patterns. Each pattern comprises a central input well and four output Wells situated at the corner of a square surrounding the input Well. The area of each pattern is five acres. The formation thickness is thirty feet, the depth of the formation is 1,000 feet and the original petroleum oil in place is 1,500 barrels per acre foot. Referring particularly to `FIGUR-l2", 2, there is illustrated the field containing a plurality of the developed five-spot patterns. The wells are indicated by numbered circles. Input wells are indicated by circles having two slanting lines connected thereto and output well-s are indicated by plain circles. The numerals within the circles indicate the time sequence in which the wells can be drilled and the numerals within the patterns indicate the time sequences of operating the patterns. The letters A to M at the midpoints of each group of four well patterns signified by numerals 1, 2, 3, and 4 indicates the time sequence of operating each group of patterns.

lIn-situ combustion operations are begun in Pattern No. 1A. This pattern consists of the linput well, indicated` by the numeral 1 within the circle and the numeral 1 adjacent thereto, and the four output wells, indicated by the circles containing the numerals 1, in the upper left-hand corner of the four tive-spot patterns designated by the letter A. Com-bustion is initiated in this pattern and oxidizing fluid is injected into the input well. Ordinarily, the oxidizing lluid wil-l be air and hereinafter Where the term air is used, it will be intended to include any oxidizing fluid. Referring particularly to FIGURE 1, air is injected into the input well initially at a rate of about 500,000 standard cubic feet per day. This rate of injection is maintained lfor approximately 40 days, as indicated by the line labeled Pattern 1A. Thereafter, the rate of air injection is gradually increased. At the end of 100 days, the rate has increased to about 1,330,000 standard cubic feet per day. At the end of 150 days, the rate is about 2,500,000 standard cubic feet per day and at the end of 200 days is about 3,750,000 standard cubic feet per day. Shortly after 250 days, the rate is maintained constant at about 5,250,000 standard cu bic feet per day until 400 days have elapsed. This is the maximum rate of air injection for Pattern No. 1A. After this time, the rate of air injection into the input well is gradually decreased. At 450 days, the rate is decreased to about 5,000,000 standard cubic feet per day and at 500 days the rate is decreased to about 2,750,000 standard cubic feet per day. At 540 days, the rate of injection is about 500,000 standard cu-bic feet per day and this rate is maintained until 600 days have elapsed. Injection of air into the input well is discontinued at 600 days.

`One-hundred and fifty days lfollowing initiation of combustion and injection of air into Pattern No. 1A, initiation of combustion and injection of air is begun in Pattern No. 2A. Pattern No. 2A is the pattern adjoining the right side of Pattern No. 1A and comprises the input well, indicated by the numeral 1 within the circle and the numeral 2 adjacent thereto, and the surrounding four wells indicated by the circles containing the numerals 1.

.In Pattern No. 2A, injection of air is begun, similarly as in Pattern No. 1A, at a rate of about 500,000 standard cubic feet per day. This rate of injection is maintained for approximately the next 40 days, 190 days following the beginning of operations in Well Pattern No. 1A, as indicated by the line labeled Pattern No. 2A. Thereafter, the rate of air injections is gradually increased. At

3. the end of days following the beginning of injection of air into Pattern No. 2A, or 250 days following the beginning of operations in lPattern No. 1A, the rate is about 1,330,000 standard `cubic feet per day. At days, or 300 days following the beginning of operations in Pattern No. 1A, the rate is about 2,500,000 standard cubic feet per day and at 200 days, 0r 350 days following the beginning of operations in Pattern No. 1A, the rate is about 3,750,000 standard cubic feet per day. Shortly after 250 days of injecting air into Pattern No. 1A, or 400 days after the beginning of operations in Pattern No. 1A, the rate is leveled oft and is maintained constant at about 5,250,000 standard cubic feet per day. This is the maximum rate of air injection for Pattern No. 2A and is maintained until about 400 days of operation in Pattern No. 2A. Thereafter, the rate of air injection is gradually decreased. At 450 days following beginning of operations in Pattern No. 2A, the rate is decreased to about 5,000,000 standard cubic feet per day, and at 500 days the rate is decreased to about 2,750,000 standard cubic feet per day. At 540 days, tne rate of injection is about 500,000 standard `cubic feet per day and this rate is maintained constant until 600 days following initiation of operations in Pattern No. 2A have elapsed. Injection of air is discontinued at the end of 600 days following the beginning of operations in Pattern No. 2A. This is 750 days following the beginning of operations in Pattern No. 1A and 15 0 days following cessation of operations in Pattern No. 1A.

Three hundred day-s subsequent to the beginning of operations in Pattern No. 1A, and 150 days subsequent to the beginning of operations in Pattern No. 2A, initiation of combustion and injection of air is begun in Pattern No. 3A. Pattern No. 3A is the pattern adjoining and below Pattern No. 1A. The input well of Pattern No. 3A is indicated by the numeral 1 in the circle having the adjacent numeral 3. Each of the four output wells is indicated by the circles containing the numerals 1. The air injection rate in Pattern No. 3A, at the beginning of oper.- ations, is the same las in Patterns Nos. 1A and 2A, namely, about 500,000 standard cubic yfeet per day. Subsequently, as indicated by the line labeled Pattern No. 3A, the rate of air injection is gradually increased until it reaches a maximum, is maintained at this maximum for a time, and is thereafter decreased. The rates of air injection with respect to time sequence are precisely the same for Pattern No. 3A as for Patterns No. 1A and No. 2A. At the end of 600 days following initiation of operations in Pattern No. 3A, injection of air is discontinued. This is 900 days following the beginning of operations in Pattern No. 11A and 750 days following the beginning of operations in Pattern No. 2A. This is also 300 days following cessation of operations in Pattern No. 1A and 150 days following cessation of operations in Pattern No. 2A.

Thereafter, Pattern No. 4A, Pattern No. 1B, Pattern No. 2B, Pattern No. 3B, Pattern No. 4B, Pattern No. 5A, etc. are operated in the same manner as previously described for Patterns Nos. liA, 2A, and 3A. Operations in each pattern are begun 150 days subsequent to the beginning of operations in the preceding pattern and each pattern is operated for 600 days. The time sequence for each of the patterns follows the alphabetical sequence of the letters indicating each group of four patterns of FIGURE 2. Thus, for each group of four patterns labeled by a letter, operations are begun in Pattern 1, followed by Patterns 2, 3, and d, and operations in Pattern B follow Pattern A, in Pattern C follow Pattern B, in Pattern D follow Pattern C, in Pattern E follow Pattern D, etc.

In FIGURE 2, twelve groups of four patterns, namely, Patterns A to M, are shown. With operations being initiated in each pattern 150 days subsequent to initiation of operations in the preceding pattern, and 600 days being required to complete operations in each pattern, a time of 21 years will be required to complete operations in the 48 patterns. With each pattern consisting of 5 acres,

the field will contain 240 acres and operations will be complete in the field at the end of this time.

A single compressor can be employed for injection of air into the input wells, assuming sufficient capacity can be obtained with a single compressor. In the alternative, a battery of single compressors can be employed. The compressor plant can be located near the center of the field in which operations are conducted and air injection piping and oil collection lines can be shifted from time to time across the field as operations progress from one pattern to another.

It will be appreciated that, as operations progress from one pattern to the next, the various input and output wells can be drilled as needed. The numerals within the circles representing the wells in FIGURE 2 indicate the year, beginning with operations in Pattern No. 1A, that the well can be drilled. Thus, the wells for Patterns Nos. IA, 2A, and 3A may be drilled the first year. In the second year, the input well and one of the output wells for Pattern No. 4A and the input well and two of the outputV wells for Pattern No. 1B may be drilled. In the third year, the input Wells and four of the output wells for Patterns 2B, 3B, and 4B may be drilled. Thereafter, the wells would be drilled similarly in the time sequence indicated in the figure.

With the beginning of operations in Pattern No. 2A, 150 days following the beginning of operations in Pattern No. 1A, the total cumulative rate of air injection for both of these patterns will, of course, be the sum of the rates of air injection for each pattern. The total cumulative air injection rate at the end of 150 days of operation in Pattern No. 1A and the beginning of operations in Pattern No. 2A, thus, is 3,000,000 standard cubic feet per day. At the end of 200 days, the total cumulative air injection rate is 4,200,000 standard cubic feet per day. At the end of 300 days, operations are begun in Pattern No. 3A and at this time the total cumulative air injection rate is the sum of the individual air injection rates in Patterns Nos. 1A, 2A, and 3A. Thus, at the end of 300 days following initiation of operations in Pattern No. 1A, the total cumulative air injection rate is 8,000,000 standard cubic feet per day. Thereafter, as the rate of air injection is increased in Patterns Nos. 2A and 3A, the total cumulative air injection rate for the three patterns increases. At the end of 450 days following initiation of operations in Pattern No. 1A, operations are begun in Pattern No. 4A. At this time, the total cumulative air injection rate will be the air injection rate for the four patterns and will be about 12,500,000 standard cubic feet per day. The air injection rate in Pattern No. 1A at this time is beginning to decrease, the air injection rate in Pattern No. 2A will have leveled olf, and the air injection rate for Pattern No. 3A will increase. Shortly thereafter, namely, 465 days following initiation of operations in Pattern No. 1A, the total cumulative air injection rate reaches a maximum. This maximum is about 12,800,000 standard cubic feet of air per day. Subsequently, with decrease of the air injection rate in Pattern No. 1A and the maintenance of the initial air injection rate in Pattern No. 4A, the total cumulative air injection rate decreases. It decreases thereafter to a minimum, at 540 days, of about 11,800,000 standard cubicl feet of air per day. Thereafter, as indicated in FIGURE 1, it begins to increase. At no time, with sequences of 150 days between the initiation of operations in the individual well patterns,

will there be more than four patterns operating simultaneously. The total cumulative air injection rate for the four patterns thus being operated is indicated in FIG- URE 1 by the line labeled Total Cumulative Air Injection for Four Patterns.

The maximum air injection rate for any one individual pattern is approximately 5,250,000 standard cubic feet of air per day. With injection of air simultaneously into four patterns and each pattern being operated with the maximum air injection rate at one time, a compressor capacity capable of providing 21,000,000 standard cubic feet of air per day would be required. On the other hand, as indicated in the embodiment illustrated in FIGURES 1 and 2, the maximum air injection rate at any one time will be 12,800,000 standard cubic feet per day. Accordingly, the capacity of the air compressor, being operated in accordance with the procedure of the invention, need be only about 62% of the compressor capacity that would otherwise be required.

Other well patterns, and well patterns having other areas, than the one described above may be treated similarly in accordance with the invention. Further, the rates of injection of the air may be different than those described above depending upon the formation thickness, the rates of migration of the combustion front, the amount of hydrocarbon material within the formation, and other factors. Additionally, the time sequence of beginning operations in the various well patterns and the total time of operation in each of the patterns, as well as the number of patterns being operated simultaneously, may be different.

Having thus described our invention, it will be understood that such description has been given by way of illustration and example and not by way of limitation, reference for the latter purpose being had to the appended claims.

We claim:

1. In a process for the recovery of hydrocarbon material fro-m a subterranean formation containing hydrocarbon material wherein said formation is penetrated by a plurality of wells, said wells forming a plurality of similar patterns and each of said patterns having input means including at least one input well and output means including at least one output well, and a fluid is injected under pressure from a compressor means into said formation through an input means of a pattern and said hydrocarbon material is thereby displaced from said formation and moved into the direction of said output means of said pattern from which output means it is recovered, the steps for establishing and maintaining substantially constant the rate of injection of said fluid into said formation from said compressor means comprising (1) injecting said fluid under pressure from said compressor means into said formation through the input means of a first pattern at a rate sufficiently high to displace said hydrocarbon material from said formation and move said hydrocarbon material in the direction of the output means of said rst pattern,

(2) gradually increasing the rate of injection of said fluid through said input means of said first pattern,

(3) discontinuing increase in the rate of injection of said fiuid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said first pattern can be recovered from said output means of said pattern,

(4) thereafter gradually decreasing the rate of injection of said fluid through said input means of said first pattern,

(5) at a time subsequent to step (1) but prior to step (3) injecting said fluid under pressure from said compressor means into said formation through the input means of a second pattern and displacing hydrocarbon material from said formation in the direction of the output means of said second pattern,

(6) gradually increasing the rate of injection of said fluid through said input means of said second pattern,

(7) discontinuing increase in the rate of injection of said fluid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said second pattern can be recovered from said output means of said pattern,

(8) thereafter gradually decreasing the rate of injection of said Huid through said input means of said second pattern, and

(9) thereafter in seriatim for each of the other patterns carrying out steps (6), (7), and (8), the time interval in step (5) being such that step (5) is carried out for any one pattern coincidentally with step (6), for at least one other pattern until the cumulative rate of injection of said fluid from said compressor means into said formation through the input means of said plurality of well patterns has reached a maximum.

2. The process of claim l wherein said patterns are five-spot patterns having as input means one input well and as output means four equidistantly spaced output wells surrounding said input well.

3. In a process for the recovery of hydrocarbon material from a subterranean formation containing hydrocarbon material wherein a fluid is injected under pressure from a compressor means into said formation through an input means and hydrocarbon material is thereby displaced from the formation and moved into the direction of an output means from which output means it is recovered, the steps for establishing and maintaining substantially constant the rate of injection of said fluid into said formation from said compressor means comprising (l) drilling into said formation a plurality of wells to form a first pattern having input means including at least one input well and output means including at least one output well,

(2) injecting said liuid under pressure from said compressor means into said formation through said input means of said first pattern at a rate sufliciently high to displace said hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means of said first pattern,

(3) gradually increasing the rate 0f injection of said fluid through said input means of said first pattern,

(4) discontinuing increase in the rate of injection of said fluid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said first pattern can be recovered from said output means of said pattern,

(5) thereafter gradually decreasing the rate of injection of said fiuid through said input means of said first pattern,

(6) drilling into said formation a plurality of wells to form a second pattern having input means including at least one input well and output means including at least one output Well, said second pattern being similar to said tirst pattern,

(7) at a time subsequent to step (2) but prior to step (4) injecting said fiuid under pressure from said compressor means into said formation through said input means of said second pattern at a rate suiciently high to displace said hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means of said second pattern,

(8) gradually increasing the rate of injection of said fluid through said input means of said second pattern,

(9) discontinuing increase in the rate of injection of said fiuid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said second pattern can be recovered from said output means of said pattern,

(10) thereafter gradually decreasing the rate of injection of said fluid through said input means of said second pattern, and

(1l) thereafter in seriatim drilling into said formation a plurality of wells to form other patterns having input means including at least one input well and output means including at least one output well, each of said patterns being similar to said first pattern,

and for each of said other patterns carrying out Steps (7), (S), (9), and (l0), the time interval in step (7) being such that step (7) is carried out for any one pattern coincidentally with step (8) for at least one other pattern until the cumulative rate of injection of said fiuid from said compressor means into said formation through said input means of said plurality of well patterns has reached a maxilTillIl.

4. In a process for the recovery of hydrocarbon material from a subterranean formation containing hydrocarbon material wherein said formation is penetrated by a plurality of wells, said wells forming a plurality of similar patterns and each of said patterns having input means including at least one input well and output means including at least one output well, and combustible material within said formation is ignited, an oxidizing fluid is injected under pressure from a compressor means into said formation through an input means of a pattern, and a combustion front migrates through said formation and hydrocarbon material is thereby displaced from said formation and moved into the direction of said output means of said pattern from which output means it is recovered, the steps for establishing and maintaining substantially constant the rate of injection of said oxidizing fluid into said formation from said compressor means comprising (1) igniting combustible material within said formation between the input means and the output means of a first pattern and injecting said oxidizing fiuid under pressure from said compressor means into said formation through said input means of said first pattern at a rate suiciently high to effect displacement of hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means of said first pattern,

(2) gradually increasing the rate of injections of said oxidizing tiuid through said input means of said first pattern,

(3) discontinuing increase in the rate of injection of said oxidizing fluid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said first pattern can be recovered from said output means of said pattern,

(4) gradually decreasing the rate of injection of said oxidizing fiuid through said input means of said first pattern,

(5) at a time subsequent to step (l) but prior to step (3) igniting combustible material within said formation between the input means and the output means of a second pattern and injecting said oxidizing fluid under pressure from said compressor means into said formation through said input means of said second pattern at a rate sufficiently high to effect displacement of hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means of said second pattern,

(6) gradually increasing the rate of injection of said oxidizing uid through said input means of Said second pattern,

(7) discontinuing increase in the rate of injection of said oxidizing fluid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said second pattern can be recovered from said output means of said pattern,

(8) thereafter gradually decreasing the rate of injection of said oxidizing iiuid through said input means of said second pattern, and

(9) thereafter in seriatim for each of the other patterns carrying out steps (5), (6), (7), and (8), the time interval in step (5) being such that step (5) is 9 carried out for any one pattern coincidentally with step (6) for at least one other pattern until the cumulative rate of injection of said oxidizing iiuid from said compressor means into said formation through said input means of said plurality of well patterns has reached a maximum.

5. The process of claim 4 wherein said patterns are five-spot patterns having as input means one input well and as output means four equidistantly spaced output wells surrounding said input well.

6. In a process for the recovery of hydrocarbon material from a subterranean formation containing hydrocarbon material wherein combustible material within said formation is ignited, an oxidizing fluid is injected under pressure from a compressor means into said formation through an input means, and a combustion front migrates through said formation and hydrocarbon material is thereby displaced from said formation and moved into the direction of an output means from which it is recovered, the steps for establishing and maintaining substantially constant the rate of injection of said oxidizing fluid into said formation from said compressor means cornprising (l) drilling into said formation a plurality of wells to form a first pattern having input means including at least one input well and output means including at least one output well,

(2) igniting combustible material within said formation between the input means and the output means of said first pattern and injecting said oxidizing fluid under pressure from said compressor means into said formation through said input means of said rst pattern at a rate sufficiently high to elfect displacement of hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means of said irst pattern,

(3) gradually increasing the rate of injection of said oxidizing fluid through said input means of said first pattern,

(4) discontinuing increase in the rate of injection of said oxidizing uid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said first pattern can be recovered from said output means of said pattern,

(5) thereafter gradually decreasing the rate of injection of said oxidizing fluid through said input means of said first pattern,

(6) drilling into said formation a plurality of Wells to form a second pattern having input means including at least one input Well and output means including at least one output well, said second pattern being similar to said rst pattern,

(7) at a time subsequent to step 2) but prior to step (4) igniting combustible material within said formation between the input means and the output means of said second pattern and injecting said oxidizing fluid under pressure from said compressor means into said formation through said input means of said second pattern at a rate sufficiently high to effect displacement of hydrocarbon material from said formation and move said hydrocarbon material in the direction of said output means,

(8) gradually increasing the rate of injection of said oxidizing fluid through said input means of said second pattern,

(9) discontinuing increase in the rate of injection of said oxidizing fluid before the rate at which said hydrocarbon material is displaced from said formation exceeds the rate at which the entire amount of said displaced hydrocarbon material from said second pattern can be recovered from said output means of said pattern,

(10) thereafter gradually decreasing the rate of injection of said oxidizing uid through said input means of said second pattern, and

(l1) thereafter in seriatim drilling into said formation a plurality of wells to form other patterns having input means including at least one input well and output means including at least one output well, each of said patterns being similar to said first pattern, and for each of said other patterns carrying out steps (7), (8), (9), and (l0), the time interval in step (7) being such that step (7) is carried out for any one pattern coincidentally with step (8) for at least one other pattern until the cumulative rate of injection of said oxidizing uid from said compressor means into said formation through said input means of said plurality of well patterns has reached a maximum.

7. The process of claim 6 wherein said patterns are live-spot patterns having as input means one input well and as output means four equidistantly spaced output wells surrounding said input well.

References Cited in the file of this patent UNITED STATES PATENTS Simrn Nov. 27, 1956 Henning Sept. 29, 1959 OTHER REFERENCES UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTIGN Patent No. 3, 126,953 March 3l 1964 Theodore We Nelson et al,

It :lesv hereby certified that error appears in the above numbered. patent requiring correction and that the said Letters Patent shouldl read as corrected below.

Column 3, line 27, for "indicates" read indicate column 3, line 75, and column 8, line 36, for "injections", each occurrence, read injection column lO, line 44, for "Henning" read Hennig Signed and sealed this 15th day of September 1964.,

(SEAL' Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. IN A PROCESS FOR THE RECOVERY OF HYDROCARBON MATERIAL FROM A SUBTERRANEAN FORMATION CONTAINING HYDROCARBON MATERIAL WHEREIN SAID FORMATION IS PENETRATED BY A PLURALITY OF WELLS, SAID WELLS FORMING A PLURALITY OF SIMILAR PATTERNS AND EACH OF SAID PATTERNS HAVING INPUT MEANS INCLUDING AT LEAST ONE INPUT WELL AND OUTPUT MEANS INCLUDING AT LEAST ONE OUTPUT WELL, AND A FLUID IS INJECTED UNDER PRESSURE FROM A COMPRESSOR MEANS INTO SAID FORMATION THROUGH AN INPUT MEANS OF A PATTERN AND SAID HYDROCARBON MATERIAL IS THEREBY DISPLACED FROM SAID FORMATION AND MOVED INTO THE DIRECTIN OF SAID OUTPUT MEANS OF SAID PATTERN FROM WHICH OUTPUT MEANS IT IS RECOVERED, THE STEPS FOR ESTABLISHING AND MAINTAINING SUBSTANTIALLY CONSTANT THE RATE OF INJECTION OF SAID FLUID INTO SAID FORMATION FROM SAID COMPRESSOR MEANS COMPRISING (1) INJECTING SAID FLUID UNDER PRESSURE FROM SAID COMPRESSOR MEANS INTO SAID FORMATION THROUGH THE INPUT MEANS OF A FIRST PATTERN AT A RATE SUFFICIENTLY HIGH TO DISPLACE SAID HYDROCARBON MATERIAL FROM SAID FORMATION AND MOVE SAID HYDROCARBON MATERIAL IN THE DIRECTION OF THE OUTPUT MEANS OF SAID FIRST PATTERN, (2) GRADUALLY INCREASING THE RATE OF INJECTION OF SAID FLUID THROUGH SAID INPUT MEANS OF SAID FIRST PATTERN, (3) DISCONTINUING INCREASE IN THE RATE OF INJECTION OF SAID FLUID VEFORE THE RATE AT WHICH SAID HYDROCARBON MATERIAL IS DISPLACED FORM SAID FORMATION EXCEEDS THE RATE AT WHICH THE ENTIRE AMOUNT OF SAID DISPLACED HYDROCARBON MATERIAL FROM SAID FIRST PATTERN CAN BE RECOVERED FRM SAID OUTPUT MEANS OF SAID PATTERN (4) THEREAFTER GRADUALLY DECREASING THE RATE OF INJECTION OF SAID FLUID THROUGH SAID INPUT MEANS OF SAID FIRST PATTERN, 